The characteristic feature of aldehydes regarding the carbonyl group’s attachment is that it is always located at the end of the carbon chain. In an aldehyde functional group, the carbon of the carbonyl group is bonded to a hydrogen atom and is also attached to the rest of the molecule through a single bond. The general structure of an aldehyde is R-CHO, where R represents an alkyl or aryl group. This arrangement distinguishes aldehydes from ketones, where the carbonyl group is situated within the carbon chain. The presence of a hydrogen atom on the carbonyl carbon is a defining feature of aldehydes.